I found it really straightforward- just time and patience. I was laying over floorboards so just overlaid with 6mm ply, securing 150mm centres. I posted here with some links to tools/skim coat that I used. With the skim coat I just used a plasterers towel to spread it across the ply and then sanded down any imperfections.
In terms of adhesive I've always used F44 without any issues. You can get small tubs of it as well which is handy as it goes quite a long way.
I'd be wary of the places that advertise the same flooring cheaper. I had a few problems with another company who were advertising karndean in stock at a slightly cheaper price but it wasn't, and they were really bad at replying to any emails (funnily enough just searched for them and look like they have closed down now) and took a while to get my money back.
I recently had to replace some herringbone LVT. I had to use a heat gun to lift the staves. I used F44 and the notched trowel. It went well. From memory, the customer had to pay for 2.5L. She only needed about 0.5L, but it is what it is
It’s a High temp and has fibres so it won’t move at all. The best glue if any sunlight on the floor.
F44 is decent but only use it for polysafe these days.